1. Field of the Invention
The present invention relates to a lipping tool for lipping an acetabular reamer, and, more particularly, to a lipping tool and method that can be used on a range of sizes of acetabular reamers.
2. Description of the Related Art
A hip joint prosthesis requires preparation of the acetabulum by milling a precision shape therein using an acetabular reamer. A typical acetabular reamer has a hollow hemispherical shell shape with apertures in the hemispherical shell. The hemispherical shell is attached to a shaft which can be inserted into a rotating tool such as a drill thereby providing rotation of the acetabular reamer, and hence, the motive force for the milling operation. The apex of the hemispherical shell typically is along the shaft longitudinal axis.
The apertures in the hemispherical shell have a dual purpose. Firstly, an edge of each aperture is formed outwardly, respective to the shell center, to form a cutting tooth or cutting surface. The forming of the aperture edge outwardly is referred to as a lipping operation. Secondly, the apertures allow milled tissue to collect in the shell interior, thereby providing a somewhat self-cleaning aspect to the milling operation. The apertures and cutting surfaces are located on the shell to provide approximately 180° cutting coverage during rotation of the acetabular reamer thereby allowing a uniform milling of the acetabulum.
Variation in the size of the acetabulum for the human population requires a range of sizes of acetabular reamers, a specific size of the acetabular reamer being determined by the hip joint size of the person undergoing hip joint prosthesis. The different sizes of acetabular reamers is generally specified by different radii of curvature, or diameters, of the hemispherical shell.
A known type of acetabular reamer is sometimes referred to as a “cheese grater” style which looks like a hemispherical cheese grater with typically circular apertures therein. A portion of the circumference of each aperture is lipped outwardly forming cutting surfaces or cutting teeth, and having a peak therein. There are at least three problems with this style of reamer. Firstly, the hemispherical cut in the acetabulum produced by the peaked teeth can be rough. Secondly, the cheese grater style reamer with peaked teeth cuts poorly at the apex of the acetabular reamer. Thirdly, a large number of these relatively small teeth are required to ensure complete 180° cutting coverage during rotation of the acetabular reamer thereby allowing a uniform milling of the acetabulum. Past attempts to make acetabular reamers with longer non-peaked cutting teeth, to overcome the problems stated above, have required frequent manufacturing setups.
One of the challenges associated with manufacturing an acetabular reamer is the setup, or changeover, time required for the lipping operation. Setup generally includes a change in tooling, materials and/or operating parameters for a machine used in a given manufacturing operation. A specific machine may be used to perform the lipping operation on a variety of acetabular reamer sizes. Given past methods of lipping the cutting surfaces, particularly relatively long non-peaked cutting surfaces, and the different radii of curvature for different sizes of acetabular reamers, a setup was required when a machine prepared for use with a different acetabular reamer size than was just previously lipped on that machine. Setup is inherently lost productive time for a lipping operation in that no lipping of acetabular reamers can occur during setup.
What is needed in the art is tooling and a method for lipping cutting surfaces on a range of acetabular reamer sizes that can lip relatively long cutting surface in a non-peaked manner, reduces or completely eliminates setup time for a lipping operation and thereby maximizes productive time on a machine used for a lipping operation, reduces manufacturing costs per reamer, increases reamer manufacturing throughput and increases the return on investment for a machine and tooling used for lipping.